1. Field of the Invention
The present invention relates to a method and apparatus for measuring and designing an electric circuit and a computer-readable recording medium for recording the same. In particular, the present invention relates to a method and an apparatus for measuring an electric circuit such as an oscillator circuit, an amplifier circuit or the like based on S-parameters of a 2-port network thereof, a method and an apparatus for designing the electric circuit, a computer-readable recording medium recording a method of measuring the electric circuit, and a computer-readable recording medium for recording a method of designing the electric circuit.
2. Description of the Related Art
Oscillators in RF (Radio Frequency) and microwave frequencies remain to be rather mysterious circuit blocks, that is, their behaviors are not fully explained yet. In order to analyze a microwave oscillator, an approach of calculating oscillation parameters by introducing a virtual ground into an equivalent circuit of the microwave oscillator has been heretofore proposed (for exmaple, a prior art document 1, Stanilaw Alechno, xe2x80x9cAnalysis Method Characteristics Microwave Oscillators, Oscillator Analysis, Part 1xe2x80x9d, Microwave and RF, November 1997; a prior art document 2, Stanilaw Alechno, xe2x80x9cAnalysis Method Characteristics Microwave Oscillators, Oscillator Analysis, Part 2xe2x80x9d, Microwave and RP, December 1997; a prior art document 3, Stanilaw Alechno, xe2x80x9cAnalysis Method Characteristics Microwave Oscillators, Oscillator Analysis, Part 3xe2x80x9d, Microwave and RF, January 1998; and a prior art document 4, Stanilaw Alechno, xe2x80x9cAnalysis Method Characteristics Microwave Oscillators, Oscillator Analysis, Part 4xe2x80x9d, Microwave and RF, February 1998).
However, in particular, designing a wide-tuning voltage-controlled oscillator (hereinafter, a voltage-controlled oscillator is referred to as a VCO) still involves a lot of guesses, many printed-circuit board tunes, even with the help of today""s highly sophisticated design tools. One problem in the designing process lies in the absence of analysis method that gives full insights into oscillation phenomenon represented in an easy-to-understand format.
Traditionally, all oscillators are classified into either a negative resistance oscillator (also known as a reflection oscillator) or a feedback oscillator. The criterion is whether or not there is an xe2x80x9cobviousxe2x80x9d feedback circuit. In RF and microwave frequencies, it becomes difficult to construct a feedback circuit without introducing excess phase shift. Therefore, almost all oscillators in the frequency range are classified as a negative resistance oscillator.
FIG. 1A is a circuit diagram showing a circuit of a negative resistance oscillator of the prior art, and FIG. 1B is a circuit diagram showing a reflection analysis model circuit, showing a method of analyzing the negative resistance oscillator.
As shown in FIG. 1B, the negative resistance oscillator is represented as a combination of an active element part 10 and a resonator part 20 of a passive element. For example, an active element of a transistor TR generates a negative resistance, and drives a passive element, which is usually a resonator RE. Simply speaking, when the negative resistance beats all losses in the resonator RE and the active element, oscillation builds up. Oscillation conditions for reflection analysis shown in FIG. 1B are expressed by the following Equations (1) and (2):
|xcex93Axc2x7xcex93B|xe2x89xa71xe2x80x83xe2x80x83(1); 
and 
arg(xcex93A)=xe2x88x92arg(xcex93B)xe2x80x83xe2x80x83(2), 
where xcex93A denotes a reflection coefficient of a port P11 when viewing the active element part 10 from the port P11, xcex93B denotes a reflection coefficient of a port P12 when viewing the resonator part 20 from the port P12, and arg(xc2x7) denotes a phase or an angle of deviation of an argument thereof.
In the prior art, negative resistance analysis is so common, yet there are many questions in controversy as to the validity of this analysis. Also there are some oscillation parameters, like a loaded-Q, that cannot be derived from this analysis. The loaded-Q is one of the fundamental yet most important parameters because it dictates spectral purity (indicating how low phase noise is). Missing loaded-Q information when analyzing an oscillator prevents designers from a full understanding of their own design. In other words, there is such a problem that there is not yet any method of analyzing an RF circuit and a microwave circuit in a complete form.
It is an essential object of the present invention to overcome the foregoing problems, and also to provide a method and an apparatus for measuring an electric circuit, capable of measuring circuit parameters by analyzing an electric circuit such as an RF circuit, a microwave circuit or the like in a complete form using a method simpler than that of the prior art.
It is another object of the present invention to provide a method and an apparatus for designing an electric circuit, capable of designing circuit parameters by analyzing an electric circuit such as an RF circuit, a microwave circuit or the like in a complete form using a method simpler than that of the prior art.
It is a still further object of the present invention to provide a computer-readable recording medium for recording a program for measuring an electric circuit or a method of designing an electric circuit, capable of measuring or designing circuit parameters by analyzing an electric circuit such as an RF circuit, a microwave circuit or the like in a complete form using a method simpler than that of the prior art.
According to one aspect of the present invention, there is provided a method of measuring an electric circuit including the steps of:
entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
calculating S-parameters of the generated 2-port network; and
calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters.
The above-mentioned method preferably further includes the step of calculating characteristic parameters of the electric circuit in accordance with the calculated open-loop transfer function.
Also, the above-mentioned method preferably further includes the steps of:
entering other element value of at least one of the plurality of elements of the entered equivalent circuit; and
repeatedly executing the step of specifying, the step of generating and the two steps of calculating for the equivalent circuit of the electric circuit containing the other element value.
Further, the above-mentioned method preferably further includes the steps of:
entering other element value of at least one of the plurality of elements of the entered equivalent circuit; and
repeatedly executing the step of specifying, the step of generating and the three steps of calculating for the equivalent circuit of the electric circuit containing the other element value.
In the above-mentioned method, the electric circuit is preferably an oscillator, and the characteristic parameters are at least one of an oscillation frequency, a gain margin, a phase margin and a loaded-Q.
In the above-mentioned method, the electric circuit is preferably an amplifier circuit, and the characteristic parameters are at least one of a maximum gain within a 3-dB bandwidth, the 3-dB bandwidth and a stability factor.
According to another aspect of the present invention, there is provided an apparatus for measuring an electric circuit comprising:
entering means for entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying means for specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating means for generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
first calculating means for calculating S-parameters of the generated 2-port network; and
second calculating means for calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters.
The above-mentioned apparatus preferably further comprises third calculating means for calculating characteristic parameters of the electric circuit in accordance with the calculated open-loop transfer function.
Also, the above-mentioned apparatus preferably further comprises outputting means for displaying or printing data with respect to the calculated open-loop transfer function.
Further, the above-mentioned apparatus preferably further comprises outputting means for displaying or printing data with respect to the calculated characteristic parameters.
According to a further aspect of the present invention, there is provided a method of designing an electric circuit including the steps of:
entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
calculating S-parameters of the generated 2-port network;
calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters;
calculating characteristic parameters of the electric circuit in accordance with the calculated open-loop transfer function; and
specifying an element whose element value to be changed among the plurality of elements of the equivalent circuit of the electric circuit, and calculating element values of the equivalent circuit when the characteristic parameters of the electric circuit become desired characteristic parameters.
In the above-mentioned method, the electric circuit is preferably an oscillator, and the characteristic parameters are at least one of an oscillation frequency, and a loaded-Q.
In the above-mentioned method, the electric circuit is preferably an amplifier circuit, and the characteristic parameters are at least one of a maximum gain within a 3-dB bandwidth and the 3-dB bandwidth.
According to a still further aspect of the present invention, there is provided an apparatus for designing an electric circuit comprising:
entering means for entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying means for specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating means for generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
first calculating means for calculating S-parameters of the generated 2-port network;
second calculating means for calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters;
third calculating means for calculating characteristic parameters of the electric circuit in accordance with the calculated open-loop transfer function; and
fourth calculating means for specifying an element whose element value to be changed among the plurality of elements of the equivalent circuit of the electric circuit, and calculating element values of the equivalent circuit when the characteristic parameters of the electric circuit become desired characteristic parameters.
The above-mentioned apparatus preferably further comprises outputting means for displaying or printing at least one of the calculated open-loop transfer function of the electric circuit, the calculated characteristic parameters of the electric circuit, and the calculated element value of the equivalent circuit when the characteristic parameters of the electric circuit become the desired characteristic parameters.
According to a more still further aspect of the present invention, there is provided a computer-readable recording medium for recording a program for measuring an electric circuit, including the steps of:
entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
calculating S-parameters of the generated 2-port network; and
calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters.
According to a still more further aspect of the present invention, there is provided a computer-readable recording medium for recording a program for designing an electric circuit, including the steps of:
entering an equivalent circuit of the electric circuit, the equivalent circuit comprising a plurality of elements respectively having element values thereof;
specifying a break point and a virtual ground in the entered equivalent circuit, the break point being for disconnecting an electric path for forming a closed-loop circuit;
generating a 2-port network by disconnecting the electric path at the specified break point in the entered equivalent circuit so as to form first and second terminals that are two ends of the electric path, the 2-port network having a first port comprising the first terminal and the specified virtual ground, and having a second port comprising the second terminal and the specified virtual ground;
calculating S-parameters of the generated 2-port network;
calculating an open-loop transfer function of the electric circuit in accordance with the calculated S-parameters;
calculating characteristic parameters of the electric circuit in accordance with the calculated open-loop transfer function; and
specifying an element whose element value to be changed among the plurality of elements of the equivalent circuit of the electric circuit, and calculating element values of the equivalent circuit when the characteristic parameters of the electric circuit become desired characteristic parameters.